dafeizei(站内联系TA):cry::cry::cry:pl_zzu(站内联系TA)In order to lower the temperature the most effective protocol is to add R4NX
(X = Cl,Br) and use an aqueous solvent with K2CO3 as the base.For alkenes,which
do not contain an electron withdrawing group then halide free conditions,achieved by
either using aryl or vinyl triflates as the electrophile or adding a halide sequestering
agent (Ag+) for aryl or vinyl halides,will be advantageous.
Heck 反应通常是在无水条件下进行的,溶剂一般
选用DMF,MeCN,MeOH 等,辅以季铵等表面活性剂.
最早的催化剂是PdCl2 或Pd(OAc)2,但反应过程中会产
生钯黑,影响反应效率; 之后研究发现,苯基膦作为配
体可以稳定催化剂钯,但催化剂与产物的分离很困难.
所以有人开始研究采用水溶性配体使之不易在有机溶
剂中溶解,从而兼具均相和多相催化剂的优点.这类
水溶性配体主要有Scheme 18 中几种类型.
由于采用水溶性配体,选用纯水或含水混合溶剂的